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Blasted into space from a giant air gun

When Jules Verne wrote about a gigantic gun that could be used to launch people into space in the 19th century, no one expected it to become a reality. Now physicist John Hunter has outlined the design of such a gun that he says could slash the cost of putting cargo into orbit.

The gun is based on a smaller device Hunter helped to build in the 1990s while at the Lawrence Livermore National Laboratory (LLNL) in California. With a barrel 47 metres long, it used compressed hydrogen gas to fire projectiles weighing a few kilograms at speeds of up to 3 kilometres per second.

Now Hunter and two other ex-LLNL scientists have set up a company called Quicklaunch, based in San Diego, California, to create a more powerful version of the gun.

At the Space Investment Summit in Boston last week, Hunter described a design for a 1.1-kilometre-long gun that he says could launch 450-kilogram payloads at 6 kilometres per second. A small rocket engine would then boost the projectile into low-Earth orbit.

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Huge g-forces

While humans would clearly be killed and conventional satellites crushed by the gun’s huge g-forces, it could lift robust payloads such as rocket fuel. Finding cheap ways to transport fuel into space will lower the cost of keeping the International Space Station in orbit, and in future it may be needed to supply a crewed mission to Mars.

The gun would cost &dollar;500 million to build, says Hunter, but individual launch costs would be lower than current methods. “We think it’s at least a factor of 10 cheaper than anything else,” he says.

Franklin Chang-Diaz, a former astronaut and physicist at the Ad Astra Rocket Company based in Webster, Texas, says a launch gun might make more sense on the moon, where there is no atmosphere. “You don’t have to worry about drag or heating or anything like that,” he says.

Welder’s torch

Hunter acknowledges that the projectile would be slowed by its passage through Earth’s atmosphere. But he says drag would be minimal on a pointy-nosed projectile, causing it to slow by only half a kilometre per second.

He also admits that the heat generated by the high-speed passage through the atmosphere is “like a welder’s torch”. However, it would be relatively short-lived, he says, with the projectile clearing the atmosphere in less than 100 seconds. Designing the projectile so that it could survive having some layers of its outer skin burned off would get around this problem, Hunter says.